重组竹的单轴与纯剪应力应变关系

Stress-strain relationship of parallel strand bamboo under uniaxial or pure shear load

重组竹是将竹丝束平行组坯、经高压胶合而成的一种生物质复合材料,是一种极具潜势的建筑结构材料。研究重组竹的基本力学性能和应力应变关系,是建立此类材料本构关系和进行重组竹结构非线性分析的基础。将重组竹理想化为横向各向同性复合材料,通过试验,给出了重组竹各主轴方向的单轴与各主平面的纯剪力学参数,建立了各种应力状态下的应力应变关系。结果表明,重组竹力学性能优于常用的结构用木材,且变异性较小。重组竹顺纹受拉强度约是顺纹受压强度的2倍;横纹受拉强度远远低于横纹受压强度;横切面内的剪切模量及强度远远低于另外两个方向,且横纹剪切强度是顺纹剪切强度的3倍。重组竹的应力应变关系和破坏模式与纤维参与受力程度密切相关。顺纹受拉时,拉应力完全由纤维承担,破坏表现为纤维的脆性拉断,强度最高,应力应变为完全线性关系;其他应力状态下,破坏均发生在基体或纤维-基体界面,若裂纹的扩展受到纤维限制,破坏呈渐进性,强度较低,应力应变曲线由早期的线性关系转入后期的非线性关系;当裂纹的扩展未受到纤维限制,破坏强度最低,应力应变呈线性关系。

Parallel Strand Bamboo（PSB）is a biocomposite composed of long narrow parallel bamboo strands which are adhesively bonded under high pressure.It has more and more attractive structural applications in building and construction engineering.It＇s important to well understand the stress-strain relationship to develop the constitutive law and conduct the nonlinear analysis of PSB structures.The PSB was treated as an transversely isotropic composite in the experiment and the uniaxial parameters in each main material axis and the pure shearing parameters in each main material plane were proposed,and the corresponding stressstrain relationships of each stress state were also established.The results show that compared with common used woods in construction engineering,PSB has higher strengths with less variability.Strengthof tension parallel to grain is nearly as twice as that of compression parallel to grain.In perpendicular to grain direction,the strength of tension is much lower than the that of compression.Shearing in transverseto-grain plane presents lowest modulus and strength than those shearing in other two directions.The shearing strength in perpendicular to grain is as about 3times as that of shearing in parallel to grain direction.The stress-strain relationships and the failure modes of PSB are significantly depended on the way in which the fiber participated.In parallel to grain direction,tensile damage almost entirely contributes to the broken of fibers,which shows the highest strength and brittle behavior among all stress states.In other cases,when the expending of failure cracks are restricted by fibers,the damage presents progressive process and higher strength,and the stress-strain relationships exhibit linearity in the earliear life while turn to nonlinearity in the later life of the specimens.When damages take place in matrix or in fiber-matrix interface without fibers involved in,the material shows lower strength,and the stress-strain curves present linear and brittle behavior.